1. Field of the Invention
Kilns in which chemical transformation of bulk materials occur continuously as combustion gases flow along the kiln axis, counter to a flow of input feed, frequently operate with the feed stock suspended in a water slurry. In such kilns, particularly cement kilns, the escaping combustion gases entrain a sizeable percentage of finely divided product. The field of this invention is that of reducing the Mount of product which leaves the kiln entrained in the stream of exhaust gas.
2. Description of Prior Art
A typical wet-process rotary kiln constructed according to the present state of the art is a long cylindrical shell rotated about its axis and tilted about two degrees from horizontal so the material fed into it tends to flow downward and the counterflowing gases from a system of burners exit at the upper end. The liquid slurry enters the kiln at the higher end and loses its moisture in a relatively short distance as it progresses toward the burner-and-product-discharge end.
Product is basically in the form of clinkers or chunks of reacted feed stock, but the tumbling of these clinkers during their progress along the bulk of the kiln length ensures a copious supply of product dust at the lower, exit end of the kiln. Standard practice is to fasten loops of chain to the interior kiln wall, near the slurry entrance. The resulting forest of chains, in which some are for the moment at the top of the rotating kiln, others drooping with the lower part of the loop in slurry flowing along the bottom, and still others fully immersed in the slurry, serves two purposes. Heat passes from the flowing combustion gases into the metal of the chains and from there (when that chain is at or near the bottom of the kiln) into the slurry, saving energy. Further, the ascending chains are wet, so the aforementioned dust (product) collects on them, is largely returned to the slurry as the kiln rotates, and is recycled through the kiln, undergoing the thermal process again.
The physical arrangement described above comprises the prior art. Approximately 11 percent of the product still leaves the kiln entrained in exhaust combustion gases and must be recovered by electrostatic precipitators or equivalent means.